Agricultural expansion and flooding in plains

A study, which will undoubtedly generate controversy, has examined whether agricultural expansion, with the change in land use that this entails, increases the incidence of flooding.

Research has focused on the South American plains.

The study is the work of Javier Houspanossian’s team, from the Environmental Studies Group of the National Council for Scientific and Technical Research (CONICET), as well as from the Department of Geology at the National University of San Luis (UNSL), all of these entities in Argentina.

The results of the study indicate that the loss of deep-rooted native vegetation, as well as decreased evapotranspiration due to rapid agricultural expansion in the South American plains, have led to shallow groundwater tables and increased flooding throughout the region.

These findings reveal the hydrological impacts and possible escalation of flood risks associated with the expansion of rainfed agriculture at subcontinental and decadal scales, and improve understanding of hydrological changes in other regions of the world experiencing similar landscape changes.

Rising global demand for cereals is leading to the rapid conversion of vast swaths of native South American grassland and forest to agricultural land. Although these flat sedimentary landscapes harbor some of the most productive soils on Earth, their hydrology is particularly sensitive to disturbances in water balance introduced by changes in land and water use.

However, the hydrological impacts of the rapid expansion of rainfed agriculture in these regions are poorly understood, with attendant sustainability challenges and unknown potential risks.

Two agricultural producers talk in a flooded agricultural area, in San Luis, in 2018. (Photo: Silvina Chávez (UNSL))

According to Javier Houspanossian and colleagues, the extent and speed of agricultural expansion in the South American lowlands region over the past 40 years provides an unprecedented natural laboratory for evaluating the effects of rainfed agriculture on hydrology. .

Combining remote sensing data and in situ groundwater monitoring observations, Houspanossian and his colleagues found that as crops replaced native vegetation and grasslands, flooding in the region gradually became larger, more expansive, and more receptive to precipitation events, especially since the year 2000.

Furthermore, the findings show that the water table went from deep (between 12 and 6 meters below the surface) to shallow (between 4 and 0 meters) due to agricultural land conversion.

Houspanossian and colleagues, using data from field studies and simulations, suggest that decreased rooting depths and evapotranspiration associated with the shift from native to agricultural plant regimes could explain this hydrological transformation.

“The findings presented here are critical for future land use policies that support smarter and more integrated agriculture, water management, and rural populations,” the study authors stress.

The study is titled “Agricultural expansion raises groundwater and increases flooding in the South American plains”. And it has been published in the academic journal Science. (Source: AAAS)